Inkjet printing system and driving method thereof

ABSTRACT

An inkjet printing system is provided, which comprises: a stage on which a substrate including at least two alignment keys is mounted; an inkjet head device disposed above the stage; and an alignment key sensing device disposed above the stage, wherein the inkjet head device comprises a head unit including an inkjet head, and a supporting unit which supports the head unit and scanning the substrate in a first direction, and wherein the alignment key sensing device comprises: at least two alignment key sensors for sensing positions of the alignment keys; a sensor supporting unit for supporting the at least two alignment key sensors; and a sensor position adjustment device for adjusting positions of the alignment key sensors with respect to the alignment key sensing device.

This application is a continuation-in-part application of U.S.application Ser. No. 11/373,759 filed Mar. 10, 2006, which claimspriority to Korean Patent Application No. 10-2005-0036989, filed on May3, 2005 and all the benefits accruing therefrom under 35 U.S.C. §119,the contents of which in their entirety are herein incorporated byreference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an inkjet printing system and a drivingmethod of the inkjet printing system. More particularly, the presentinvention relates to an inkjet printing system for precisely formingcolor filters or light emitting members on a substrate and a drivingmethod of the inkjet printing system.

(b) Description of the Related Art

Inkjet printing systems are used for forming organic light emittingmembers of organic light emitting displays (“OLED”s), color filters andalignment layers for liquid crystal displays (“LCD”s), and so on.

The inkjet printing systems for forming the color filters, alignmentlayers, or organic light emitting members include a head unit and aninkjet head attached to the head unit. The inkjet head has a pluralityof nozzles. Thereby, the inkjet printing systems deposit ink or othermaterial through the nozzles into desired areas on an insulatingsubstrate to form the colors filters, alignment layers, or organic lightemitting members.

At this time, for accurately depositing the inks or other material,alignment of the inkjet head is required.

As a size of a mother glass which is divided into a plurality of cellsrespectively used as substrates for panels of display devices becomeslarger, the number of cells is increased and thereby the time foraligning the head unit and the inkjet head increases.

BRIEF SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, an inkjetprinting system comprises: a stage on which a substrate including atleast two alignment keys is mounted; an inkjet head device disposedabove the stage; and an alignment key sensing device disposed above thestage, wherein the inkjet head device comprises a head unit including aninkjet head, and a supporting unit which supports the head unit andscanning the substrate in a first direction, and wherein the alignmentkey sensing device comprises: at least two alignment key sensors forsensing positions of the alignment keys; a sensor supporting unit forsupporting the at least two alignment key sensors; and a sensor positionadjustment device for adjusting positions of the alignment key sensorswith respect to the alignment key sensing device.

The sensor position adjustment device may move the alignment key sensorsso that a straight line connecting the at least two alignment keysensors may be substantially vertical to the first direction.

The sensor position adjustment device may move the alignment key sensorsin two directions which are substantially parallel to a surface of thestage and are substantially vertical to each other with respect to thealignment key sensing device.

The inkjet head device may further comprise a horizontal transportingportion that moves the head unit in a second direction which issubstantially perpendicular to the first direction.

The alignment key sensing device may further comprise at least twosensor transporting portions moving the at least two alignment keysensors in a second direction which is substantially perpendicular tothe first direction.

According to another exemplary embodiment of the present invention, aninkjet printing system comprises: a stage on which a substrate ismounted; a head unit disposed above the stage; a supporting unitsupporting the head unit and scanning the substrate in a firstdirection; and a horizontal transporting portion moving the head unitaccording to the supporting unit, wherein the head unit comprises atleast one inkjet head, and a head position adjustment device adjusting aposition of the inkjet head with respect to the head unit.

The head position adjustment device may move the inkjet head in twodirections which are substantially parallel to a surface of the stageand are substantially vertical to each other with respect to the headunit.

The head position adjustment device may adjust the position of theinkjet head while the supporting unit scanning the substrate.

According to another exemplary embodiment of the present invention, aninkjet printing system comprises: a stage on which a substrate ismounted; a head unit which is disposed above the stage and comprises atleast one inkjet head; an upper sensor disposed above the stage; asupporting unit supporting the head unit and the upper sensor andscanning the substrate in a first direction; a horizontal transportingportion moving the head unit according to the supporting unit; a sensortransporting portion moving the upper sensor according to the supportingunit; and a lower sensor disposed outside of the stage.

The inkjet head may comprise a plurality of nozzles, and the lowersensor may sense at least one of a position of the nozzles, a distancebetween the nozzles, and an inclination angle of the inkjet head.

According to an exemplary embodiment of the present invention, analigning method of an inkjet printing system comprising: a stage; aninkjet head device including a head unit and a supporting unitsupporting the head unit; and an alignment key sensing device includingat least two alignment key sensors, a sensor supporting unit supportingthe at least two alignment key sensors, and a sensor position adjustmentdevice, comprises: mounting a substrate including at least two alignmentkeys on the stage; sensing the alignment keys using the alignment keysensors and aligning the substrate on the stage; examining a firstdirection in which the supporting unit scans the substrate and ink isprinted; adjusting positions of the alignment key sensors with respectto the alignment key sensing device using the sensor position adjustmentdevice; and realigning the substrate.

The adjusting positions of the alignment key sensors may compriseadjusting the sensor position adjustment device so that a straight lineconnecting the at least two alignment key sensors may be substantiallyvertical to the first direction.

The adjusting positions of the alignment key sensors may comprise movingthe alignment key sensors in two directions which are substantiallyparallel to a surface of the stage and are substantially vertical toeach other with respect to the alignment key sensing device.

The inkjet head device may further comprise a horizontal transportingportion that moves the head unit in a second direction which isperpendicular to the first direction.

The alignment key sensing device may further comprise at least twosensor transporting portions moving the at least two alignment keysensors in a second direction which is substantially perpendicular tothe first direction.

According to another exemplary embodiment of the present invention, analigning method of an inkjet printing system comprising: comprising: astage; a head unit including at least one inkjet head and a headposition adjustment device; and a supporting unit supporting the headunit, comprises: mounting a substrate on the stage; determining a firstdirection to print on the substrate; printing on the substrate drivingthe inkjet head and the supporting unit; and reducing an error distancebetween the first direction and a printed direction by adjusting aposition of the inkjet head with respect to the head unit using the headposition adjustment device.

The printing on the substrate and the adjusting of the position of theinkjet head with the head position adjustment device may be performedsimultaneously.

The adjusting of the position of the inkjet head may comprise moving theinkjet head in two directions which are substantially parallel to asurface of the stage and are substantially vertical to each other withrespect to the head unit.

According to another exemplary embodiment of the present invention, analigning method of an inkjet printing system comprising: a stage; a headunit including at least one inkjet head which includes a plurality ofnozzles; an upper sensor; a supporting unit supporting the head unit andthe upper sensor; a horizontal transporting portion moving the head unitaccording to the supporting unit; a sensor transporting portion movingthe upper sensor according to the supporting unit; and a lower sensordisposed outside of the stage, comprises: mounting a substrate on thestage; determining a reference position by matching positions of theupper sensor and the lower sensor; sensing at least one of a position ofthe nozzles, a distance between the nozzles, and an inclination angle ofthe inkjet head using the lower sensor; sensing a target position to beprinted using the upper sensor; and moving the inkjet head above thetarget position to be printed.

The method may further comprise aligning the substrate on the stageusing the upper sensor.

The moving of the inkjet head above the target position to be printedmay comprise referring to information about at least one of the targetposition to be printed, the position of the nozzles, the distancebetween the nozzles, and the inclination angle of the inkjet head.

At least one of the lower sensor and the upper sensor may be a CCDcamera.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent by describing preferredembodiments thereof in detail with reference to the accompanyingdrawings, in which:

FIG. 1 is a perspective view of an exemplary embodiment of an inkjetprinting system according to the present invention;

FIG. 2 is a bottom view of an exemplary head unit of an exemplaryembodiment of an inkjet printing system according to the presentinvention;

FIG. 3 is a schematic view for demonstrating formation of color filtersusing an exemplary inkjet head of an exemplary embodiment of an inkjetprinting system according to the present invention;

FIG. 4 illustrates a state of depositing ink for forming color filtersusing an exemplary inkjet head of an exemplary embodiment of an inkjetprinting system according to the present invention;

FIG. 5 is a perspective view of another exemplary embodiment of aninkjet printing system according to the present invention;

FIG. 6 is a bottom view of an exemplary head unit of another exemplaryembodiment of an inkjet printing system according to the presentinvention;

FIG. 7 is a block diagram of an exemplary alignment key sensing unit ofanother exemplary embodiment of an inkjet printing system according tothe present invention;

FIG. 8 is a layout view of an exemplary TFT array panel of the exemplaryembodiments of an LCD according to the present invention;

FIG. 9 is a layout view of an exemplary color filter panel of exemplaryembodiments of an LCD according to the present invention;

FIG. 10 is a layout view of the exemplary embodiments of the LCD havingthe exemplary TFT array panel and the exemplary color filter panel shownin FIGS. 8 and 9 according to the present invention;

FIG. 11 is a sectional view of the exemplary LCD shown in FIG. 10 takenalong line XI-XI′;

FIG. 12 shows sectional views of the exemplary LCD shown in FIG. 10taken along line XII-XII′;

FIG. 13 is an equivalent circuit diagram of an exemplary pixel of anexemplary embodiment of an OLED display according to the presentinvention;

FIG. 14 is a schematic plan view of an exemplary display panel for anexemplary embodiment of an OLED according to the present invention;

FIG. 15 is a sectional view of the exemplary display panel shown in FIG.14 taken along line XV-XV′;

FIG. 16 is a sectional view of the exemplary display panel shown in FIG.14 taken along line XVI-XVI′.

FIG. 17 is a perspective view of an inkjet printing system according toan exemplary embodiment of the present invention;

FIG. 18 is a plane view of the inkjet printing system shown in FIG. 17;

FIG. 19 is a plane view of an inkjet printing system according to anexemplary embodiment of the present invention;

FIG. 20 is a perspective view of an inkjet printing system according toan exemplary embodiment of the present invention;

FIG. 21 is a bottom view of a head unit of the inkjet printing systemshown in FIG. 20; and

FIG. 22 is an algorithm showing a method of aligning an inkjet headusing upper and lower sensors of the inkjet printing system shown inFIG. 20.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likereference numerals refer to like elements throughout. In the drawings,the thickness of layers and regions are exaggerated for clarity.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present there between. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present. As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of the present invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Embodiments of the present invention are described herein with referenceto cross section illustrations that are schematic illustrations ofidealized embodiments of the present invention. As such, variations fromthe shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, are to be expected. Thus,embodiments of the present invention should not be construed as limitedto the particular shapes of regions illustrated herein but are toinclude deviations in shapes that result, for example, frommanufacturing. For example, a region illustrated or described as flatmay, typically, have rough and/or nonlinear features. Moreover, sharpangles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present invention.

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. Exemplary embodiments of inkjet printingsystems and driving methods of the inkjet printing systems according tothe present invention will now be described with reference to FIGS. 1 to4.

FIG. 1 is a perspective view of an exemplary embodiment of an inkjetprinting system according to the present invention, FIG. 2 is a bottomview of an exemplary head unit of an exemplary embodiment of an inkjetprinting system according to the present invention, FIG. 3 is a viewdemonstrating formation of color filters using an exemplary inkjet headof an exemplary embodiment of an inkjet printing system according to thepresent invention, and FIG. 4 illustrates a state of depositing ink forforming color filters using an exemplary inkjet head of an exemplaryembodiment of an inkjet printing system according to the presentinvention.

Referring to FIGS. 1 to 4, an inkjet printing system includes a stage500 on which a mother glass 201 is disposed, a head unit 700 spaced apredetermined distance from the stage 500 in a vertical direction, and atransporting unit 300 for transporting the head unit 700 to apredetermined position.

The mother glass 201 may be substantially planar to be supported by asubstantially planar stage 500, and is divided to produce insulatingsubstrates 210 used for panels of display devices, such as color filterpanels of liquid crystal display (“LCD”) devices, as will be furtherdescribed below. Alternatively, the stage 500 may be provided with apanel for forming display panels of organic light emitting displays(“OLED”s), as will also be further described below.

A light blocking member 220, having a plurality of openings 225, isformed on each of the insulating substrates 210.

A plurality of alignment keys 240 and 240′, respectively comprisingalignment keys 241 to 248 and 241′ to 248′, are formed on opposite sidesof each of the respective insulating substrates 210, that is, at areasoutside of the light blocking member 220.

By example only, the insulating substrates 210 and corresponding lightblocking members 220 may each have a substantially rectangular shapewith first and second parallel opposite sides. The alignment keys 240are formed on the first side of each substrate 210 in a line at apredetermined interval, and the alignment keys 240′ are formed on thesecond side opposite to the first side of each substrate 210, and thealignment keys 240′ face the corresponding alignment keys 240. The lineof alignment keys 240 and the line of alignment keys 240′ may extendsubstantially parallel to the first and second sides of each insulatingsubstrate 210. Alternatively, the lines of alignment keys 240 and 240′may extend adjacent third and fourth sides of each insulating substrate210 and each light blocking member 220.

When the light blocking member 220 is made of an organic high molecularcompound, the alignment keys 240 and 240′ are formed by exposing anddeveloping the organic material as a positive or negative type. However,if the light blocking member 220 is made of inorganic materials, andafter depositing a separate photoresist film, then the alignment keys240 and 240′ are formed on the material of the light blocking member 220by exposing, developing, and etching the inorganic material. Thealignment keys 240 and 240′ may be of a circular shape, a cross shape,or other various shapes.

The head unit 700 includes an inkjet head 400 and an alignment keyposition sensor 600.

The inkjet head 400 has a long bar-like shape, however it is not limitedto such shape. The inkjet head 400 includes a plurality of nozzles 410provided on substantially an entire lower surface thereof. Ink 5 forforming color filters for a color filter panel is deposited through thenozzles 410 on the substrate 210. In the event the inkjet printingsystem is used for providing an alignment layer or organic lightemitting members to a substrate, the nozzles 410 may provide materials,other than ink 5, to the substrate on the stage 500.

The inkjet head 400 is inclined to a predetermined angle θ with respectto the Y direction. For example, since a nozzle pitch D (a distancebetween adjacent nozzles 410) is different from a pixel pitch P (adistance between adjacent pixels to be printed), by rotating the inkjethead 400 to the predetermined angle θ, an interval between adjacent inkdeposits through the nozzles 410 and the pixel pitch P may coincide.Thus, substrates used for a display having a particular pixel pitch Pmay be accommodated by rotating the inkjet head 400 to the appropriateangle θ for proper ink deposition regardless of the difference betweenthe nozzle pitch D and the pixel pitch P.

In FIG. 2, one head unit 700 is shown, however there may be a pluralityof head units 700. Also, while the illustrated head unit 700 includesonly one inkjet head 400, a plurality of inkjet heads 400 for formingcolor filters for colors such as, but not limited to, red, green, andblue colors may be provided.

The alignment key position sensor 600 senses positions of the alignmentkeys 240 and 240′ and outputs sensing signals corresponding to thesensed positions to a transporting unit controller (not shown). Thealignment key position sensor 600 may be, for example, a charged coupleddevice (“CCD”) camera.

The transporting unit 300 includes a supporting unit 310 to space thehead unit 700 from the substrates 210 by a predetermined distance, atransporting portion 330 for transporting the head unit 700 in X and Ydirections, and an elevating unit 340 for elevating the head unit 700.

The number of alignment keys 240 and 240′ may be defined based on screenresolutions of the display devices manufactured or the number of nozzles410.

For example, when an LCD having a screen resolution of 1024×768 ismanufactured on the substrate 210 and the number of nozzles 410 of theinkjet head 400 is 128, then a color filter group having 128×768 colorfilters is formed through the nozzles 410 of the inkjet head 400 by onescan of the head unit 700 in the X direction by the transporting portion330 of the transporting unit 300. That is, the color filters of 128×768are formed into openings 225 of the light blocking member 220 formed ina pixel block of 128×768 pixels, respectively. As a result, since onescan of the head unit 700 does not form all color filters on all pixelsof the LCD, a plurality of scans of the head unit 700 are required. Inthe LCD, the total scanning number is eight (128×8=1024).

Before every scanning procedure of the head unit 700 in the X directionfor forming the color filters, an alignment procedure of the head unit700 is performed using the alignment keys 240 and 240′. Therefore, forexample, when the LCD having a screen resolution of 1024×768 ismanufactured, the alignment procedure is repeated eight times, and thusthe number of alignment keys 240 and 240′ for each respective insulatingsubstrate 210 is required to be eight. In other words, the total numberof alignment keys 240 and 240′ formed on opposite sides of eachrespective substrate 210 is sixteen. Referring to FIG. 1, since thetotal number of substrates 210 formed on the mother glass 201 is nine,the total number of the alignment keys 240 and 240′ formed on the motherglass 201 is 144 (16×9=144). The total number of alignment keys 240 and240′ formed on the mother glass 201 would thus depend on the totalnumber of substrates 210 formed on the mother glass 201, as well as onthe screen resolution of the LCD and the number of nozzles 410.

Next, an exemplary method for forming the color filters on the substrate210 using an exemplary embodiment of an inkjet printing system accordingto the present invention will be further described.

The head unit 700 is arranged over the corresponding substrate 210 bythe transporting portion 330 and elevating portion 340 of thetransporting unit 300.

The head unit 700 is transported in the X direction by the transportingportion 330 of the transporting unit 300, and the alignment key positionsensor 600 is operated. The sensor 600 generates alignment key positionsensing signals corresponding to the alignment keys 241 and 241′,respectively, and outputs the alignment key position sensing signals tothe transporting unit controller (not shown).

The transporting unit controller compares the sensing signals from thealignment key position sensor 600 with the current position of the headunit 700, generates control signals for transporting the head unit 700to the scanning start position, and outputs the control signals to thetransporting unit 300.

Thereby, the transporting portion 330 of the transporting unit 300arranges the head unit 700 to the scanning start position based on thecontrol signals from the transporting unit controller. Next, byoperating the transporting portion 330 of the transporting unit 300 andthe nozzles 410 of the inkjet head 400, the inkjet printing systemtransfers the head unit 700 in the X direction, and thereby, as shown inFIG. 4, the color filters are formed on pixels of one pixel block by ink5 deposited into the openings 225 of the light blocking member 220within the one pixel block, where a pixel block includes a matrix ofpixels, such as a subset of the total number of pixels for the display.

When the scanning of the head unit 700 for forming the color filters isfinished, the transporting portion 330 of the transporting unit 300repeats the aligning procedure of the head unit 700 for the next scan,to form color filters on the next pixel block.

In the same way as described above, the sensor 600 senses positions ofthe alignment keys 242 and 242′ adjacent to the alignment keys 241 and241′, respectively, and generates alignment key position sensing signalsto output to the transporting unit controller. The transporting unitcontroller compares positions of the alignment keys 242 and 242′,determined by the sensing signals from the sensor 600, with the currentposition of the head unit 700, and generates control signals fortransporting the head unit 700 to the scanning start position andoutputs the control signals to the transporting unit 300. Thereby, thehead unit 700 at the transporting unit 300 is moved in the X or Ydirection to be positioned at the next scanning start position.

Then, another scan of the head unit 700 is performed to form colorfilters in pixels of the next pixel block.

Whenever forming the color filters in a corresponding pixel block, theposition sensing operation of the alignment key position sensor 600 andthe position alignment and ink deposition operations of the head unit700 are repeated, to form all the color filters.

When all the color filters are formed on the corresponding substrate210, the head unit 700 is arranged over the next substrate 210 by thetransporting unit 300 and the color filter forming operation is repeatedon the next substrate 210. As a result, the color filters are formed onall the substrates 210 of the mother glass 201.

By the aligning operation of the head unit 700 using the alignment keys240 and 240′ and the sensor 600, the color filters are formed on thedesired positions of the substrates 210. Accordingly, the reliability offorming the color filters at appropriate locations on the substrates 210is increased and the manufacturing cost is decreased.

Next, referring to FIGS. 5 to 7, another exemplary embodiment of aninkjet printing system according to the present invention will bedescribed.

The structures and operations of the inkjet printing system aresubstantially the same as those of the inkjet printing system shown inFIGS. 1 to 4.

As compared with FIGS. 1 to 4, the elements performing the sameoperations are indicated by the same reference numerals, and detaileddescriptions thereof are omitted.

FIG. 5 is a perspective view of another exemplary embodiment of aninkjet printing system according to the present invention, FIG. 6 is abottom view of an exemplary head unit of another exemplary embodiment ofan inkjet printing system according to the present invention, and FIG. 7is a block diagram of an exemplary alignment key sensing unit of anotherexemplary embodiment of an inkjet printing system according to thepresent invention.

As compared with FIG. 1, an inkjet printing system shown in FIG. 5further includes an alignment key sensing unit 1000. In addition, asshown in FIG. 5, a head unit 700′ does not include the alignment keyposition sensor 600 as compared to FIG. 1.

As shown in FIGS. 5 to 7, the alignment key sensing unit 1000 includes astage 1100, an alignment key position sensor 1200 attached to the stage1100, a memory 1300 connected to the alignment key position sensor 1200,and a transporting unit controller 1400 connected to the memory 1300.

As illustrated, the stage 1100 may have a similar size and shape tothose of the mother glass 201, but the size and shape are not limitedthereto.

The alignment position sensor 1200 is a CCD camera movable in X and Ydirections of the stage 1100 by a separate controller (not shown). Formovement of the alignment position sensor 1200, moving members (notshown) may be provided on the stage 1100.

Alternatively, the alignment key position sensor 1200 may be fixed onthe stage 1100 and the position of the sensor 1200 may be varied bymovement of the stage 1100. In this case, the size and shape of thestage 1100 may be dissimilar to those of the mother glass 201, and, forexample, the size of the stage 1100 may be smaller than that of themother glass 201.

The alignment key position sensor 1200 transfers in the X or Y directionand, at the same time, senses positions of all alignment keys 240 and240′ formed on the mother glass 201 to generate a plurality of alignmentkey position sensing signals corresponding to the position of therespective alignment keys 240 and 240′. For example, each sensing signalmay have X and Y coordinate values. In FIG. 5, one alignment keyposition sensor 1200 is shown, but more than one alignment key positionsensors 1200 may be provided in alternative embodiments.

As illustrated, the alignment key sensing unit 1000 is positioned overthe head unit 700′, however, it may be positioned between the head unit700′ and the mother glass 201 for sensing purposes, and movable therebetween so as not to interfere with the printing process.

The memory 1300 stores the respective alignment key position sensingsignals from the sensor 1200. The memory 1300 may be a random accessmemory (“RAM”).

By using current position signals of the head unit 700′ and the sensedposition sensing signals of the corresponding alignment keys 240 and240′ from the memory 1300, the transporting unit controller 1400generates control signals for controlling the position of the head unit700′, and outputs the control signals to the transporting unit 300.

An exemplary forming method of the color filters using another exemplaryembodiment of the inkjet printing system according to the presentinvention will now be described.

The inkjet printing system transfers the alignment key position sensor1200 of the alignment key sensing unit 1000 in the X or Y direction, tosense positions of all the alignment keys 240 and 240′ formed on themother glass 201 for generating the alignment key position sensingsignals corresponding to the alignment keys 240 and 240′. The alignmentkey position sensing signals are stored into the memory 1300.

For a first scan of the head unit 700′ for forming the color filters ona corresponding substrate 210, the transporting unit controller 1400reads the current position signals of the head unit 700′ and the storedalignment key position sensing signals of corresponding alignment keys241 and 241′, and compares the current position of the head unit 700′with the positions of the alignment keys 241 and 241′. The transportingunit controller 1400 generates a control signal for transferring thehead unit 700′ to a scanning start position based on a comparison resultbetween the current position of the head unit 700′ and the positions ofthe alignment keys 241 and 241′ and outputs the control signal to thetransporting unit 300.

The transporting portion 330 of the transporting unit 300 transfers thehead unit 700′ to the scanning start position in accordance with thecontrol signal from the controller 1400, and moves the head unit 700′ inthe X direction to form the color filters in pixels of a first pixelblock by depositing ink 5 into openings 225 of a light blocking member220.

By repeating the above-described operations, the color filters areformed in a second pixel block adjacent to the first pixel block.

That is, the transporting unit controller 1400 reads the currentposition signals of the head unit 700′ and the stored alignment keyposition sensing signals of corresponding alignment keys 242 and 242′adjacent to the alignment keys 241 and 241′, respectively, and comparesthe current position of the head unit 700′ with the positions of thealignment keys 242 and 242′. The transporting unit controller 1400generates a control signal to move the head unit 700′ to a scanningstart position based on a comparison result and outputs the controlsignal to the transporting unit 300.

The transporting portion 330 of the transporting unit 300 transfers thehead unit 700′ to the scanning start position in accordance with thecontrol signal from the controller 1400, and moves the head unit 700′ inthe X or Y direction to form the color filters in pixels of the secondpixel block by depositing ink 5 into openings 225 of a light blockingmember 220.

The forming operations of the color filters are repeated several times,and thereby the color filters are formed in all the pixels on thecorresponding substrate 210. For example, when manufacturing the LCDhaving a screen resolution of 1024×768, the forming operation of thecolor filters as described above is repeated eight times. When theformation of color filters is finished with respect to one substrate210, the inkjet printing system transfers the head unit 700 to anothersubstrate adjacent to the substrate 210 using the transporting unit 300,and repeats the forming operations of the color filters. Thereby, thecolor filters are successively formed on all the substrates 210 formedon the mother glass 201.

Since the inkjet printing system of FIGS. 5 to 7 aligns the position ofthe head unit 700 using the alignment key sensing unit 1000 and thealignment keys 240 and 240′, the color filters are precisely formed onthe desired positions of the substrates 210. Accordingly, reliability isincreased and the manufacturing cost is decreased.

In addition, in the above embodiment of the inkjet printing system ofFIGS. 5 to 7, since the alignment key position sensor 1200 attached tothe alignment key sensing unit 1000 separately from the head unit 700senses the positions of all the alignment keys 240 and 240′ to generatethe sensing signals and stores the sensing signals into the memory 1300,and the inkjet printing system uses the stored sensing signals foraligning the position of the head unit 700, the position sensingoperation of the alignment keys 240 and 240′ is not necessary wheneverthe position of the head unit 700 is aligned. Therefore, the time forforming the color filters is reduced.

In the exemplary embodiments described above, the head unit 700 or 700′moves as a result of the sensing operation of the alignment key positionsensor 600 or 1200 to align the inkjet head 400, however, the inkjethead 400 along with the head unit 700 or 700′ or the inkjet head 400 maymove in response to a separate controller.

In addition, in the exemplary embodiments described herein, the headunit 700 or 700′ moves as a result of the sensing operation of thealignment key position sensor 600 or 1200 to align the head unit 700 or700,′ however, in alternative embodiments, the stage 500 may move inresponse to a separate transporting unit.

In the exemplary embodiments of the inkjet printing system, the headunits 700 and 700′ may be further aligned concerning positioninformation of the mother glass 201 with respect to the stage 500 usingseparate alignment keys.

Then, an inkjet printing system according to another exemplaryembodiment of the present invention in which aligning process areprecise and speedy using the above various aligning methods will bedescribed with reference to FIG. 17 to FIG. 22 sequentially. As comparedwith FIG. 1 to FIG. 4, elements performing the same operations areindicated by the same reference numerals, and detailed descriptionsthereof are omitted.

First, an inkjet printing system and an aligning method thereofaccording to an exemplary embodiment of the present invention will bedescribed with reference to FIG. 17 and FIG. 18.

FIG. 17 is a perspective view of an inkjet printing system according toan exemplary embodiment of the present invention, and FIG. 18 is a planeview of the inkjet printing system shown in FIG. 17.

An inkjet printing system according to an exemplary embodiment of thepresent invention includes a stage 500 on which a substrate 202 ismounted, an inkjet head device 1600 including a head unit 700 and atransporting unit 300, and an alignment key sensing device 1500.

At least two substrate alignment keys 2400 a and 2400 b for aligning thesubstrate 202 with respect to the stage 500 are formed at both sideregions of the substrate 202.

The head unit 700 includes at least one inkjet head (not shown), and thetransporting unit 300 includes a supporting unit 310, a horizontaltransporting portion 330, and an elevating unit 340. In the presentembodiment, the supporting unit 310 extends in the X direction so thatthe horizontal transporting portion 330 may move in the X direction. Thesupporting unit 310 may move while scanning the substrate 202 in the Ydirection. Alternatively, the stage 500 may move in the Y direction withthe supporting unit 310 fixed.

The alignment key sensing device 1500 includes a first alignment keysensor 1200 a, a second alignment key sensor 1200 b, a first sensortransporting portion 1030 a, a second sensor transporting portion 1030b, a sensor supporting unit 1010, and a sensor position adjustmentdevice (not shown).

The sensor supporting unit 1010 locates the first and second sensortransporting portions 1030 a and 1030 b at a predetermined distanceabove the substrate 202, and the sensor supporting unit 101 may move inthe Y direction while scanning the substrate 202. Alternatively, thestage 500 may move in the Y direction with the sensor supporting unit1010 fixed.

The first and second sensor transporting portions 1030 a and 1030 b movethe first and second alignment key sensors 1200 a and 1200 b in the Xdirection.

The first and second alignment key sensors 1200 a and 1200 b generatesensing signals by sensing the positions of the substrate alignment keys2400 a and 2400 b.

The sensor position adjustment device (not shown) moves the first andsecond alignment key sensors 1200 a and 1200 b in the X and Y directionswith respect to the first and second sensor transporting portions 1030 aand 1030 b. The sensor position adjustment device (not shown) may beattached to the first and second alignment key sensors 1200 a and 1200b.

Then, a method of adjusting positions of the first and second alignmentkey sensors 1200 a and 1200 b when aligning a substrate 202 on the stage500 in the inkjet printing system described above will be described withreference to FIG. 17 and FIG. 18.

First, a substrate 202 is mounted and aligned on the stage 500 accordingto a sensing signal obtained by the first and second alignment keysensors 1200 a and 1200 b which sense the positions of the substratealignment keys 2400 a and 2400 b. At this stage, the straight lineconnecting the centers of the first and second alignment key sensors1200 a and 1200 b is parallel to the first alignment line 10 c shownFIG. 18, and the straight line connecting the two substrate alignmentkeys 2400 a and 2400 b is also substantially parallel to the firstalignment line 10 c.

Next, ink is discharged onto the substrate 202 by driving the head unit700 and the nozzles (not shown) while moving the transporting unit 300of the inkjet head device 1600 in the Y direction or moving the stage500 in the Y direction. At this stage, the direction in which the ink isprinted may not be the predetermined direction even though the stage 202has been aligned on the stage 500 using the first and second alignmentkey sensors 1200 a and 1200 b. This case may be caused when thealignment keys 2400 a and 2400 b of the substrate 202 are not properlypositioned or when the second alignment line 10 h, which is thedirection the supporting unit 310 of the inkjet head device 1600 extendsand coincides with the X direction, is not parallel to the firstalignment line 10 c of the first and second alignment key sensors 1200 aand 1200 b as shown in FIG. 18. In this case, the direction determinedto print ink on the substrate 202 is not the same as the movingdirection of the head unit 700.

By adjusting the sensor position adjustment device (not shown), thepositions of the first and second alignment key sensors 1200 a and 1200b are moved in the X and Y directions, and accordingly, the movingdirection of the head unit 700 in the Y direction may coincide with thedirection to print. The straight line connecting the first and secondalignment key sensors 1200 a and 1200 b may coincide with the thirdalignment line 10 c′ which is parallel to the second alignment line 10 hof the supporting unit 310 as shown in FIG. 18.

Next, the substrate 202 is realigned on the stage 500 while sensing theposition of the substrate alignment keys 2400 a and 2400 b using thefirst and second alignment key sensors 1200 a and 1200 b which have beenrealigned.

In this way, the substrate 202 may be aligned and mounted on the stage500 and an ink may be printed on the substrate 202 exactly in a desireddirection only with a simple adjustment of positions of the first andsecond alignment key sensors 1200 a and 1200 b without changingarrangements of the inkjet printing system.

According to another embodiment of the present invention, besides thefirst and second alignment key sensors 1200 a and 1200 b, otheralignment key sensors attached to the sensor supporting unit 1010 may befurther comprised.

Then, an inkjet printing system and an aligning method thereof accordingto another embodiment of the present invention will be described withreference to FIG. 17 and FIG. 19 described above.

FIG. 19 is a plane view of an inkjet printing system according to anexemplary embodiment of the present invention.

An inkjet printing system according to the present embodiment has thesimilar structure to the inkjet printing system shown in FIG. 17 withthe alignment key sensing device.

The head unit 700 further comprises a head position adjustment device(not shown) that may move the inkjet head in the X and Y directions withrespect to the head unit 700.

When a mother substrate 201 is mounted on the stage 500 and performinginkjet printing by driving the head unit 700 and the nozzles (nowshown), the moving direction of the head unit 700 in the Y direction maynot coincide with the desired printed direction. For example, as shownin FIG. 19, the mother substrate 201 or the stage 500 may not beparallel to the printing direction 10 a of the head unit 700. Theposition of the inkjet head (not shown) may be adjusted while printingby using the head position adjustment device (not shown) such that themoving direction of the inkjet head (not shown) may coincide with thedesired printing direction 10 a′. Accordingly, the trace 50 of thedropped ink is formed in the desired printing direction 10 a′.

Besides, even in the case where errors are generated in the route of thehead unit 700 during a printing process, ink may be dropped onto theexact position of the mother substrate 201 by adjusting the position ofthe head unit 700 in the X and Y directions.

Next, an inkjet printing system and an adjusting method thereofaccording to another embodiment of the present invention will bedescribed with reference to FIG. 20 to FIG. 22

FIG. 20 is a perspective view of an inkjet printing system according toan exemplary embodiment of the present invention, and FIG. 21 is abottom view of a head unit of the inkjet printing system shown in FIG.20, and FIG. 22 is an algorithm showing a method of aligning an inkjethead using upper and lower sensors of the inkjet printing system shownin FIG. 20.

An inkjet printing system according to the present embodiment also hasthe similar structure to the inkjet printing system shown in FIG. 17.

Referring to FIG. 20, an inkjet printing system according to anexemplary embodiment of the present invention includes a stage 500 onwhich a mother substrate 201 is mounted, a supporting unit 310, ahorizontal transporting portion 330 and a sensor transporting portion1030 c which are attached to the supporting unit 310, an elevating unit340 and a head unit 700 attached to the horizontal transporting portion330, an upper sensor attached to the bottom of the sensor transportingportion 1030 c, and a lower sensor 1200 d provided outside of the stage500.

Referring to FIG. 21, the head unit 700 includes at least one inkjethead 300, which includes a plurality of nozzles 410 disposed on thebottom surface of the inkjet head 400. The inkjet head 400 may beinclined at a predetermined angle θ with respect to the Y direction.

The sensor transporting portion 1030 c is attached to the supportingunit 310 and may move in the X direction, and the lower sensor 1200 dmay move in the X and Y directions.

The description of the stage 500, the supporting unit 310, thehorizontal transporting portion 330, the elevating unit 340, and thehead unit 700 is the same as the description of the same elements of theprevious embodiment.

Then, an exemplary method of aligning the nozzles 410 of the inkjet head400 exactly to a position where ink is to be dropped will be describedwith reference to FIG. 20 to FIG. 22.

First, the upper and lower sensors 1200 c and 1200 d are moved so thatthe positions of the upper and lower sensors 1200 c and 1200 d may becoincident, which is the S1 step of FIG. 22. The coincident position ofthe lower and upper sensors 1200 c and 1200 d is stored as a referenceposition.

Next, the position of the nozzles 410 of the inkjet head 400, thedistances between the nozzles 410, and the inclination angle θ of theinkjet head 400 with respect to the Y direction are measured using thelower sensor 1200 d, which corresponds to S2 step of FIG. 22.

Next, the upper sensor 1200 c checks the alignment sate of the mothersubstrate 201 with respect to the head unit 700 and the supporting unit310 and senses coordinates of the target position Pt where ink is to bedropped or an alignment key 240 thereof with respect to the referenceposition, which corresponds to the S3 step of FIG. 22.

Next, the supporting unit 310 and the horizontal transporting portion330 are moved so that the nozzles 410 of the inkjet head 400 arepositioned above the target position Pt where ink is to be dropped,which corresponds to the S4 step of FIG. 22. At this stage, informationabout the coordinates of the target position Pt obtained by the uppersensor 1200 c, information about the positions, distances, andinclination angles of the inkjet head 400 and the nozzles 410 obtainedby the lower sensor 1200 d may be used.

The second and third steps S2 and S3 may be changed.

In this way, the nozzles 410 of the inkjet head 700 may be located onthe exact position to be printed by using the lower and upper sensors1200 c and 1200 d without performing printing.

According to another exemplary embodiment, the head unit 700 of theinkjet printing system shown in FIG. 20 may comprise a plurality ofinkjet heads 400. The lower sensor 1200 d may be used to sense thepositions of the plurality of inkjet heads 400 and determine the errordistances in the X or Y direction between the inkjet heads 400. Theerror distance in the X direction between the plurality of inkjet heads400 may be compensated by adjusting the distances between the inkjetheads 400, and the error distance in the Y direction may be compensatedby adjusting the dropping time of ink. In this way, by detecting theposition of the inkjet heads 400 using the lower sensor 1200 d that maymove in the X and Y directions, it is possible to compensate errordistances between the inkjet heads 400 without practicing inkjetprinting.

The first and second alignment key sensors 1200 a and 1200 b, and theupper and lower sensors 1200 c and 1200 d of the inkjet printing systemshown in FIG. 17 to FIG. 21 may be, for example, CCD cameras.

Substrates manufactured by using an inkjet printing system according toembodiments as such described above may be a display panel of an LCD oran OLED. When a display panel for an OLED or an LCD is produced, theinkjet printing system forms color filters for an LCD or organic lightemitting members for an OLED.

Next, an LCD using an exemplary panel manufactured by the exemplaryembodiments of the inkjet printing system according to the presentinvention will be described with reference to FIGS. 8 to 13. Theexemplary panel may be manufactured by either of the inkjet printingsystems described with respect to FIGS. 1 to 4 and FIGS. 5 to 7.

FIG. 8 is a layout view of an exemplary TFT array panel of exemplaryembodiments of an LCD according to the present invention, and FIG. 9 isa layout view of an exemplary color filter panel of exemplaryembodiments of an LCD according to the present invention. FIG. 10 is alayout view of exemplary embodiments of the LCD having the exemplary TFTarray panel and the exemplary color filter panel shown in FIGS. 8 and 9according to the present invention, FIG. 11 is a sectional view of theexemplary LCD shown in FIG. 10 taken along line XI-XI′, and FIG. 12shows sectional views of the exemplary LCD shown in FIG. 10 taken alongline XII-XII′.

As shown in FIGS. 8 to 13, an LCD includes a TFT array panel 100, acolor filter panel 200 opposite the TFT array panel 100, and an LC layer3 having LC molecules disposed between the TFT array panel 100 and thecolor filter panel 200.

First, the TFT array panel 100 will be described with reference to FIGS.8 and 10 to 12.

A plurality of gate lines 121 and a plurality of storage electrode lines131 are formed on an insulating substrate 110 of a material such as, butnot limited to, transparent glass or plastic.

The gate lines 121 transmit gate signals and extend substantially in atransverse direction, a first direction. Each of the gate lines 121includes a plurality of gate electrodes 124 projecting downward, in asecond direction, and an end portion 129 having a large area for contactwith another layer or an external driving circuit. A gate drivingcircuit (not shown) for generating the gate signals may be mounted on aflexible printed circuit (“FPC”) film (not shown), which may be attachedto the insulating substrate 110, directly mounted on the insulatingsubstrate 110, or integrated onto the insulating substrate 110.Alternatively, the gate lines 121 may extend to be connected to adriving circuit that may be directly integrated on the insulatingsubstrate 110.

The storage electrode lines 131 are supplied with a predeterminedvoltage, and each of the storage electrode lines 131 includes a stemextending substantially parallel to the gate lines 121 in the firstdirection and a plurality of pairs of storage electrodes 133 a and 133 bbranched from the stems and extending in a second direction,substantially perpendicular to the first direction. Each of the storageelectrode lines 131 is disposed between two adjacent gate lines 121, anda stem for each pixel area is positioned closer to one of the twoadjacent gate lines 121. Each of the storage electrodes 133 a and 133 bhas a fixed end portion connected to the stem and a free end portiondisposed opposite thereto on an opposite side of the pixel area. Thefixed end portion of the storage electrode 133 a has a large area, andthe free end portion thereof is bifurcated into a linear branch and acurved branch. However, the storage electrode lines 131 may have variousshapes and arrangements and are not limited to the illustrated exemplaryembodiments.

The gate lines 121 and the storage electrode lines 131 are preferablymade of an aluminum Al-containing metal such as Al and an Al alloy, asilver Ag-containing metal such as Ag and an Ag alloy, a copperCu-containing metal such as Cu and a Cu alloy, a molybdenumMo-containing metal such as Mo and a Mo alloy, chromium Cr, tantalum Ta,or titanium Ti. The gate lines 121 and the storage electrode lines 131may alternatively have a multi-layered structure including twoconductive films (not shown) having different physical characteristics.If a multi-layered structure is employed, one of the two films ispreferably made of a low resistivity metal such as an Al-containingmetal, an Ag-containing metal, and a Cu-containing metal for reducingsignal delay or voltage drop and the other film is preferably made of amaterial such as a Mo-containing metal, Cr, Ta, or Ti, which have goodphysical, chemical, and electrical contact characteristics with othermaterials such as indium tin oxide (“ITO”) or indium zinc oxide (“IZO”).Examples of the combination of the two films in a multi-layeredstructure include a lower Cr film and an upper Al (alloy) film and alower Al (alloy) film and an upper Mo (alloy) film. However, the gatelines 121 and the storage electrode lines 131 may be made of variousmetals or conductors.

The lateral sides of the gate lines 121 and the storage electrode lines131 are inclined relative to a surface of the insulating substrate 110,and the inclination angle thereof ranges about 30 to about 80 degrees.

A gate insulating layer 140 preferably made of, but not limited to,silicon nitride (SiNx) or silicon oxide (SiOx) is formed on the gatelines 121 and the storage electrode lines 131. The gate insulating layer140 may further be formed over exposed portions of the insulatingsubstrate 110.

A plurality of semiconductor stripes 151 preferably made of hydrogenatedamorphous silicon (“a-Si”) or polysilicon are formed on the gateinsulating layer 140. The semiconductor stripes 151 extend substantiallyin the longitudinal direction, the second direction parallel with thestorage electrodes 133 a and 133 b, and become wide near the gate lines121 and the storage electrode lines 131 such that the semiconductorstripes 151 cover large areas of the gate lines 121 and the storageelectrode lines 131. Each of the semiconductor stripes 151 includes aplurality of projections 154 branched out toward the gate electrodes124.

A plurality of ohmic contacts, including ohmic contact stripes andislands 161 and 165, are formed on the semiconductor stripes 151. Theohmic contact stripes and islands 161 and 165 are preferably made of n+hydrogenated a-Si heavily doped with an N-type impurity such asphosphorous, or they may be made of silicide. Each ohmic contact stripe161 includes a plurality of projections 163, and the projections 163 andthe ohmic contact islands 165 are located in pairs on the projections154 of the semiconductor stripes 151 and spaced apart from each other toform a channel on the projections 154.

The lateral sides of the semiconductor stripes 151 and the ohmiccontacts 161 and 165 are inclined relative to the surface of theinsulating substrate 110, and the inclination angles thereof arepreferably in a range of about 30 to about 80 degrees.

A plurality of data lines 171 and a plurality of drain electrodes 175are formed on the ohmic contacts 161 and 165 and the gate insulatinglayer 140.

The data lines 171 transmit data signals and extend substantially in thelongitudinal direction, the second direction, to intersect the gatelines 121. The data lines 171 are insulated from the gate lines 121 bythe gate insulating layer 140 disposed between the gate lines 121 andthe data lines 171. Each data line 171 also intersects the storageelectrode lines 131 and runs parallel between adjacent pairs of storageelectrodes 133 a and 133 b. Each data line 171 includes a plurality ofsource electrodes 173 projecting toward the gate electrodes 124 andbeing curved like a crescent, and an end portion 179 having a large areafor contact with another layer or an external driving circuit. A datadriving circuit (not shown) for generating the data signals may bemounted on an FPC film (not shown), which may be attached to theinsulating substrate 110, directly mounted on the insulating substrate110, or integrated onto the insulating substrate 110. Alternatively, thedata lines 171 may extend to be connected to a driving circuit that maybe directly integrated on the insulating substrate 110.

The drain electrodes 175 are separated from the data lines 171 anddisposed opposite the source electrodes 173 with respect to the gateelectrodes 124, thus maintaining the channel over the projection 154.Each of the drain electrodes 175 includes a wide end portion and anarrow end portion. The wide end portion overlaps a storage electrodeline 131 and the narrow end portion is partly enclosed by a sourceelectrode 173.

A gate electrode 124, a source electrode 173, and a drain electrode 175along with a projection 154 of a semiconductor stripe 151 form a TFThaving a channel formed in the projection 154 disposed between thesource electrode 173 and the drain electrode 175 and between the ohmiccontact island 165 and the projection 163 of the ohmic contact stripe161.

The data lines 171 and the drain electrodes 175 are preferably made of arefractory metal such as Cr, Mo, Ta, Ti, or alloys thereof. However, thedata lines 171 and the drain electrodes 175 may alternatively have amultilayered structure including a refractory metal film (not shown) anda low resistivity film (not shown). Examples of the multi-layeredstructure include, but are not limited to, a double-layered structureincluding a lower Cr/Mo (alloy) film and an upper Al (alloy) film, and atriple-layered structure of a lower Mo (alloy) film, an intermediate Al(alloy) film, and an upper Mo (alloy) film. However, the data lines 171and the drain electrodes 175 may be made of various metals orconductors.

The data lines 171 and the drain electrodes 175 have inclined edgeprofiles with respect to a surface of the insulating substrate 110, andthe inclination angles thereof range about 30 to about 80 degrees.

The ohmic contacts 161 and 165 are interposed only between theunderlying semiconductor stripes 151 and the overlying conductors 171and 175 thereon, and reduce the contact resistance therebetween.Although the semiconductor stripes 151 are narrower than the data lines171 at most places, the width of the semiconductor stripes 151 becomeslarge near the gate lines 121 and the storage electrode lines 131 asdescribed above, to smooth the profile of the surface, therebypreventing disconnection of the data lines 171. The semiconductorstripes 151 have almost the same planar shapes as the data lines 171 andthe drain electrodes 175 as well as the underlying ohmic contacts 161and 165. However, the semiconductor stripes 151 include some exposedportions, which are not covered with the data lines 171 and the drainelectrodes 175, such as portions located over the projections 154between the source electrodes 173 and the drain electrodes 175, thus theexposed portions form a channel.

A passivation layer 180 is formed on the data lines 171, the drainelectrodes 175, and the exposed portions of the semiconductor stripes151. The passivation layer 180 may be further formed on exposed portionsof the gate insulating layer 140 as shown. The passivation layer 180 ispreferably made of an inorganic or organic insulator and it may have aflat top surface. Examples of the inorganic insulator include, but arenot limited to, silicon nitride and silicon oxide. The organic insulatormay have photosensitivity and a dielectric constant of less than about4.0. Alternatively, the passivation layer 180 may include a lower filmof an inorganic insulator and an upper film of an organic insulator suchthat it possesses the excellent insulating characteristics of theorganic insulator while preventing the exposed portions of thesemiconductor stripes 151 from being damaged with the organic insulator.

The passivation layer 180 has a plurality of contact holes 182 and 185exposing the end portions 179 of the data lines 171 and the drainelectrodes 175, respectively. The passivation layer 180 and the gateinsulating layer 140 have a plurality of contact holes 181 exposing endportions 129 of the gate lines 121, a plurality of contact holes 183 aexposing portions of the storage electrode lines 131 near the fixed endportions of the storage electrodes 133 a, and a plurality of contactholes 183 b exposing the linear branches of the free end portions of thestorage electrodes 133 a.

A plurality of pixel electrodes 191, a plurality of overpasses 83, and aplurality of contact assistants 81 and 82 are formed on the passivationlayer 180. They are preferably made of a transparent conductor such asITO or IZO, or a reflective conductor such as Ag, Al, Cr, or alloysthereof, such as for use in a reflective LCD.

The pixel electrodes 191 are physically and electrically connected tothe drain electrodes 175 through the contact holes 185 such that thepixel electrodes 191 receive data voltages from the drain electrodes175. The pixel electrodes 191 supplied with the data voltages generateelectric fields in cooperation with a common electrode 270 of theopposing color filter panel 200 supplied with a common voltage, whichdetermine the orientations of liquid crystal molecules (not shown) of aliquid crystal layer 3 disposed between the two panels 100 and 200. Apixel electrode 191 and the common electrode 270 form a capacitorreferred to as a “liquid crystal capacitor,” which stores appliedvoltages after the TFT turns off.

A pixel electrode 191 overlaps a storage electrode line 131 includingstorage electrodes 133 a and 133 b for improving an aperture ratio ofeach pixel. The pixel electrode 191 and a drain electrode 175 connectedthereto and the storage electrode line 131 form an additional capacitorreferred to as a “storage capacitor,” which enhances the voltage storingcapacity of the liquid crystal capacitor.

The contact assistants 81 and 82 are connected to the end portions 129of the gate lines 121 and the end portions 179 of the data lines 171through the contact holes 181 and 182, respectively. The contactassistants 81 and 82 protect the end portions 129 and 179 and enhancethe adhesion between the end portions 129 and 179 and external devices,such as a gate driving circuit and a data driving circuit as previouslydescribed.

The overpasses 83 cross over the gate lines 121 and are connected to theexposed portions of the storage electrode lines 131 and the exposedlinear branches of the free end portions of the storage electrodes 133 athrough the contact holes 183 a and 183 b, respectively, which aredisposed opposite each other with respect to the gate lines 121. Thatis, each overpass 83 spans between two adjacent pixels. Thus, each pixelincludes a portion of a first overpass 83 at a lower portion of thepixel area and a portion of a second overpass 83 at an upper portion ofthe pixel area. The storage electrode lines 131 including the storageelectrodes 133 a and 133 b along with the overpasses 83 can be used forrepairing defects in the gate lines 121, the data lines 171, or theTFTs.

A description of the color filter panel 200 follows with reference toFIGS. 9 to 11.

A light blocking member 220, also termed a black matrix, for preventinglight leakage is formed on an insulating substrate 210 made of amaterial such as transparent glass or plastic.

The light blocking member 220 has a plurality of openings 225 that facethe pixel electrodes 191, and it may have substantially the same planarshape as the pixel electrodes 191. Otherwise, the light blocking member220 may include a plurality of portions facing the gate lines 121 anddata lines 171 on the TFT array panel 100 and a plurality of widenedportions facing the TFTs on the TFT array panel 100. The light blockingmember 220 functions as side walls for sealing ink 5 for color filters230 therein when manufacturing the color filter panel 200 using theexemplary embodiments of the inkjet printing system.

A plurality of color filters 230 are also formed on the substrate 210.The color filters 230 are formed using any of the exemplary embodimentsof the inkjet printing system according to the present invention. Thecolor filters 230 are formed substantially in openings 225 enclosed bythe light blocking member 220. Alternatively, the color filters 230 mayextend substantially in the longitudinal direction along the pixelelectrodes 191. The color filters 230 may each represent one of thecolors such as red, green, and blue colors, although other colors arewithin the scope of these embodiments.

An overcoat 250 is formed on the color filters 230 and the lightblocking member 220. The overcoat 250 is preferably made of an (organic)insulator for preventing the color filters 230 from being exposed andfor providing a flat surface. Alternatively, the overcoat 250 may beomitted.

A common electrode 270 is formed on the overcoat 250. The commonelectrode 270 is preferably made of a transparent conductive materialsuch as, but not limited to, ITO and IZO.

Alignment layers 11 and 21 that may be horizontal or vertical alignmentlayers are coated on inner surfaces of the panels 100 and 200, andpolarizers 12 and 22 are provided on outer surfaces of the panels 100and 200 so that their polarization axes may cross perpendicularly withrespect to each other and one of the polarization axes may be parallelto the gate lines 121. Alternatively, one of the polarizers 12 and 22may be omitted when the LCD is a reflective LCD.

The LCD may further include at least one retardation film (not shown)for compensating the retardation of the LC layer 3.

The LCD may further include a backlight unit (not shown) for supplyinglight to the LC layer 3 through the polarizers 12 and 22, theretardation film, and the panels 100 and 200.

Now, an exemplary method of manufacturing the exemplary TFT array panelshown in FIGS. 8 to 12 will be described.

A metal film is sputtered on an insulating substrate 110 made of amaterial such as transparent glass or plastic, and is patterned by wetetching or dry etching with a photoresist pattern to form a plurality ofgate lines 121 including a plurality of gate electrodes 124 and an endportion 129 and a plurality of storage electrode lines 131 having a pairof storage electrodes 133 a and 133 b.

After sequential deposition of a gate insulating layer 140, an intrinsica-Si layer, and an extrinsic a-Si layer, the extrinsic a-Si layer andthe intrinsic a-Si layer are photo-etched to form a plurality ofextrinsic semiconductor stripes and a plurality of intrinsicsemiconductor stripes 151 including a plurality of projections 154 onthe gate insulating layer 140. The gate insulating layer 140 has athickness of about 1,500 Å to about 5,500 Å, the intrinsic a-Si layerhas a thickness of about 500 Å to about 2,000 Å, and the extrinsic a-Silayer thickness is about 300 Å to about 600 Å.

A conductive layer is sputtered with a thickness of about 1,500 Å toabout 3,000 Å, and is patterned by etching with a photoresist pattern toform a plurality of data lines 171, each including a plurality of sourceelectrodes 173 and end portion 179, and a plurality of drain electrodes175.

Portions of the extrinsic a-Si layer which are not covered with the datalines 171 and the drain electrodes 175 are removed by etching tocomplete a plurality of ohmic contact stripes 161 including a pluralityof projections 163 and a plurality of ohmic contact islands 165, and toexpose portions of the intrinsic semiconductor stripes 151. Oxygenplasma treatment may follow thereafter in order to stabilize the exposedsurfaces of the semiconductor stripes 151.

A passivation layer 180 preferably made of positive photosensitiveorganic materials is deposited on the data lines 171, the drainelectrodes 175, and the exposed semiconductor stripes 151, as well asexposed portions of the gate insulating layer 140.

The passivation layer 180 is exposed to light through a photo mask. Thephoto mask includes a transparent substrate and an opaque light blockingfilm, and it is divided into light transmitting areas, light blockingareas, and translucent areas. The light blocking film is not disposed onthe light transmitting areas, but it is disposed on the light blockingareas and the translucent areas. The light blocking film exists as awide area having a width larger than a predetermined value on the lightblocking areas, and it exists as a plurality of areas having width ordistance smaller than a predetermined value to form slits.

The passivation layer 180 is developed to form a plurality of contactholes 182 and 185 exposing the end portions 179 of the data lines 171and the drain electrodes 175. The passivation layer 180 is alsodeveloped along with the gate insulating layer 140 to form the contactholes 181, 183 a, and 183 b exposing the end portions 129 of the gatelines 121, and the storage electrodes 133 a and 133 b of the storageelectrode lines 131, respectively.

When the passivation layer 180 is made of negative photosensitivematerials, the positions of the light transmitting areas and the lightblocking areas of the photo mask are changed with each other.

Finally, IZO or ITO with a thickness of about 400 Å to about 500 Å issputtered and etched to form a plurality of pixel electrodes 191, aplurality of contact assistants 81 and 82, and overpasses 83 on thepassivation layer 180, the exposed drain electrodes 175, the endportions 179 of the data lines 171, the end portions 129 of the gatelines 121, and the exposed storage electrode lines 131. The alignmentlayer 11 may be provided on the TFT array panel 100 using an inkjetprinting system or other method.

While exemplary embodiments of an LCD, and an exemplary TFT array panel100 and an exemplary color filter panel 200 for an LCD, have beendescribed, it should be understood that the exemplary embodiments of theinkjet printing system according to the present invention may beutilized to form color filters 230 on other embodiments of LCDs notdescribed herein.

Next, an OLED display using a panel manufactured by the exemplaryembodiments of the inkjet printing system according to the presentinvention will be described with reference to the accompanying drawings.

First, an exemplary OLED display according to the present invention isdescribed with reference to FIG. 13.

FIG. 13 is an equivalent circuit diagram of an exemplary pixel of anexemplary embodiment of an OLED display according to the presentinvention.

Referring to FIG. 13, an OLED display includes a plurality of signallines 121, 171, and 172 and a plurality of pixels PX connected theretoand arranged substantially in a matrix.

The signal lines 121, 171, and 172 include a plurality of gate lines121, a plurality of data lines 171, and a plurality of voltagetransmission lines 172.

The gate lines 121 transmit gate signals (or scanning signals), extendsubstantially in a row direction, first direction, and are substantiallyparallel to each other. The data lines 171 transmit data signals, extendsubstantially in a column direction, second direction, and aresubstantially parallel to each other and substantially perpendicular tothe gate lines 121. The voltage transmission lines 172 transmit drivingvoltages, extend substantially in the column direction, and aresubstantially parallel to each other and substantially parallel to thedata lines 171.

Each pixel PX includes a switching transistor Qs, a driving transistorQd, a storage capacitor Cst, and an organic light emitting element LD.

The switching transistor Qs has a control terminal corresponding to agate connected to the gate line 121, an input terminal corresponding toa source connected to the data line 171, and an output terminalcorresponding to a drain connected to the driving transistor Qd. Theswitching transistor Qs transmits the data signal applied to the dataline 171 to the driving transistor Qd in response to the scanningsignal, otherwise termed gate signal, applied to the gate line 121.

The driving transistor Qd has a control terminal connected to theswitching transistor Qs, an input terminal connected to the voltagetransmission line 172, and an output terminal connected to the lightemitting element LD. The driving transistor Qd flows a current having amagnitude depending on a voltage applied between the control terminaland the output terminal thereof.

The storage capacitor Cst is connected between the control terminal andthe output terminal of the driving transistor Qd. The storage capacitorCst charges and maintains the data signal applied to the controlterminal of the driving transistor Qd from the switching transistor Qs.

The light emitting element LD has an anode connected to the outputterminal of the driving transistor Qd and a cathode connected to acommon voltage Vcom. The light emitting element LD emits light having anintensity depending on an output current I_(LD) of the drivingtransistor Qd.

The switching transistor Qs and the driving transistor Qd are N-channelfield effect transistors (“FETs”). Alternatively, at least one of thetransistors Qs and Qd may be a P-channel FET. While a particularconfiguration has been shown, the connections between the transistors Qsand Qd, the capacitor Cst, and the light emitting element LD may bemodified, and such modifications are within the scope of theseembodiments.

Now, a structure of an exemplary display panel for an exemplaryembodiment of the OLED according to the present invention will bedescribed with reference to FIGS. 14 to 16.

FIG. 14 is a schematic plan view of an exemplary display panel for anexemplary embodiment of an OLED according to the present invention, FIG.15 is a sectional view of the exemplary display panel shown in FIG. 14taken along line XV-XV′, and FIG. 16 is a sectional view of theexemplary display panel shown in FIG. 14 taken along line XVI-XVI′.

A plurality of gate conductors that include a plurality of gate lines121 including first gate electrodes 124 a and second gate electrodes 124b are formed on an insulating substrate 110. The insulating substrate110 may be formed from a material such as, but not limited to,transparent glass or plastic. The first and second gate electrodes 124 aand 124 b may also be termed control electrodes.

The gate lines 121 transmit gate signals and extend substantially in atransverse direction, a first direction. Each of the gate lines 121includes an end portion 129 having a large area for contact with anotherlayer or an external driving circuit. The first gate electrodes 124 aproject upward from the gate lines 121. A gate driving circuit (notshown) for generating the gate signals may be mounted on a flexibleprinted circuit (“FPC”) film (not shown), which may be attached to theinsulating substrate 110, directly mounted on the insulating substrate110, or integrated onto the insulating substrate 110. Alternatively, thegate lines 121 may extend to be connected to a driving circuit that maybe directly integrated on the insulating substrate 110.

Each of the second gate electrodes 124 b is separated from the gatelines 121 and disposed between two adjacent gate lines 121. Each secondgate electrode 124 b includes a storage electrode 127 that extendsdownwardly from the second gate electrode 124 b in a second direction,turns to the right towards a side of a pixel, and then extendslengthwise back upwardly in the second direction. The storage electrode127 may extend substantially a full length of a pixel.

The gate conductors 121 and 124 b, that include the gate lines 121 andthe first and second gate electrodes 124 a and 124 b, are preferablymade of an Al containing metal such as Al and Al alloy, a Ag containingmetal such as Ag and Ag alloy, a Cu containing metal such as Cu and Cualloy, a Mo containing metal such as Mo and Mo alloy, Cr, Ti or Ta. Thegate conductors 121 and 124 b may have a multi-layered structureincluding two films having different physical characteristics. In such amulti-layered structure, one of the two films is preferably made of lowresistivity metal including an Al containing metal, an Ag containingmetal, or a Cu containing metal for reducing signal delay or voltagedrop in the gate conductors 121 and 124 b, and the other film ispreferably made of material such as Cr, Mo, Mo alloy, Ta, or Ti, whichhas good physical, chemical, and electrical contact characteristics withother materials such as ITO or IZO. Examples of the combination of thetwo films include a lower Cr film and an upper Al (alloy) film and alower Al (alloy) film and an upper Mo (alloy) film. However, the gateconductors 121 and 124 b may be made of various metals or conductors.

The lateral sides of the gate conductors 121 and 124 b are inclinedrelative to a surface of the insulating substrate 110, and theinclination angle thereof ranges about 30 to about 80 degrees.

A gate insulating layer 140 preferably made of silicon nitride (SiNx) orsilicon oxide (SiOx) is formed on the gate conductors 121 and 124 b. Thegate insulating layer 140 may be further formed on exposed portions ofthe insulating substrate 110.

A plurality of semiconductor islands 154 a and 154 b preferably made ofhydrogenated a-Si or polysilicon are formed on the gate insulating layer140. The semiconductor islands 154 a and 154 b are disposed on the firstand second gate electrodes 124 a and 124 b, respectively.

A plurality of pairs of first and second ohmic contact islands 163 a and163 b and a plurality of pairs of third and fourth ohmic contact islands165 a and 165 b are formed on the semiconductor islands 154 a and 154 b,respectively. The ohmic contact islands 163 a, 163 b, 165 a, and 165 bare preferably made of n+ hydrogenated a-Si heavily doped with an N-typeimpurity such as phosphorous, or they may be made of silicide.

The first ohmic contact islands 163 a and 165 a are disposed on thefirst semiconductor island 154 a and separated from each other in pairand the second ohmic contact islands 163 b and 165 b are disposed on thefirst semiconductor island 154 a and separated from each other in pair.

The lateral sides of the semiconductor islands 154 a and 154 b and theohmic contacts 163 a, 163 b, 165 a, and 165 b are inclined relative tothe surface of the insulating substrate 110, and the inclination anglesthereof are preferably in a range of about 30 to about 80 degrees.

A plurality of data conductors including a plurality of data lines 171,a plurality of voltage transmission lines 172, and a plurality of outputelectrodes 175 a and 175 b are formed on the ohmic contacts 163 a, 163b, 165 a, and 165 a and the gate insulating layer 140.

The data lines 171 for transmitting data signals extend substantially inthe longitudinal direction, the second direction, and intersect the gatelines 121 substantially perpendicularly. The data lines 171 may beinsulated from the gate lines 121 by the gate insulating layer 140. Eachdata line 171 may include a plurality of first input electrodes 173 aprojecting toward the first gate electrode 124 a and an end portion 179having a large area for contact with another layer or an externaldriving circuit. A data driving circuit (not shown) for generating thedata signals may be mounted on a FPC film (not shown), which may beattached to the insulating substrate 110, directly mounted on theinsulating substrate 110, or integrated into the insulating substrate110. Alternatively, the data lines 171 may extend to be connected to adriving circuit that may be directly integrated in the insulatingsubstrate 110.

The voltage transmission lines 172 for transmitting driving voltages forthe driving transistor Qd extend substantially in the longitudinaldirection, second direction, and intersect the gate lines 121 and extendparallel to the data lines 171. Each voltage transmission line 172includes a plurality of second source electrodes 173 b projecting towardthe second gate electrode 124 b. The voltage transmission lines 172 mayoverlap the storage electrodes 127 and be connected to each other.

The first and second drain electrodes 175 a and 175 b are separated fromeach other and separated from the data lines 171 and the voltagetransmission lines 172. The first and second drain electrodes 175 a and175 b may also be termed output electrodes.

The first source electrodes 173 a, which are input electrodes, aredisposed opposite the first drain electrodes 175 a with respect to thefirst gate electrodes 124 a and the second source electrodes 173 b,which are input electrodes, are disposed opposite the second drainelectrodes 175 b with respect to the second gate electrodes 124 b.

The data conductors 171, 172, 175 a, and 175 b are preferably made of arefractory metal such as Cr, Mo, Ta, Ti, or alloys thereof. However,they may have a multilayered structure including a refractory metal film(not shown) and a low resistivity film (not shown). Examples of themulti-layered structure include a double-layered structure including alower Cr/Mo (alloy) film and an upper Al (alloy) film and atriple-layered structure of a lower Mo (alloy) film, an intermediate Al(alloy) film, and an upper Mo (alloy) film. However, data conductors171, 172, 175 a, and 175 b may be made of various metals or conductors.

Like the gate conductors 121 and 124 b, the lateral sides of the dataconductors 171, 172, 175 a, and 175 b are inclined relative to a surfaceof the insulating substrate 110, and the inclination angle thereofranges about 30 to about 80 degrees.

The ohmic contacts 163 a, 163 b, 165 a, 165 b are interposed onlybetween the underlying semiconductor islands 154 a and 154 b and theoverlying data conductors 171, 172, 175 a, and 175 b thereon and reducethe contact resistance there between. The semiconductor islands 154 aand 154 b include some exposed portions, which are not covered with thedata conductors 171, 172, 175 a, and 175 b, such as portions locatedbetween the source electrodes 173 a and 173 b and the drain electrodes175 a and 175 b, and between the ohmic contact islands 163 a and 163 band the ohmic contact islands 165 a and 165 b, thus forming channelsthere between on the semiconductor islands 154 a and 154 b.

A passivation layer 180 is formed on the data conductors 171, 172, 175a, and 175 b and the exposed portions of semiconductor islands 154 a and154 b. The passivation layer 180 may further be formed on the exposedportions of the gate insulating layer 140. The passivation layer 180 ispreferably made of inorganic or organic insulator and it may have a flattop surface. Examples of the inorganic insulator include silicon nitrideand silicon oxide. The organic insulator may have photosensitivity anddielectric constant less than about 4.0. The passivation layer 180 mayinclude a lower film of inorganic insulator and an upper film of organicinsulator, such that it possesses the excellent insulatingcharacteristics of the organic insulator while preventing the exposedportions of the semiconductor islands 154 and 154 b from being damagedby the organic insulator.

The passivation layer 180 has a plurality of contact holes 182, 185 a,and 185 b exposing the end portions 179 of the data lines 171 and thefirst and second drain electrodes 175 a and 175 b, respectively. Thepassivation layer 180 and the gate insulating layer 140 have a pluralityof contact holes 181 and 184 exposing the end portions 129 of the gatelines 121 and the second gate electrodes 124 b, respectively.

A plurality of pixel electrodes 191, a plurality of connecting members85, and a plurality of contact assistants 81 and 82 are formed on thepassivation layer 180. They are preferably made of a transparentconductor such as ITO or IZO or a reflective conductor such as Ag, Al,Cr, or alloys thereof.

The pixel electrodes 191 are physically and electrically connected tothe second drain electrodes 175 b through the contact holes 185 b. Theconnecting members 85 are physically and electrically connected to thesecond gate electrodes 124 b and the first drain electrodes 175 athrough the contact holes 184 and 185 a, respectively.

The contact assistants 81 and 82 are physically and electricallyconnected to the end portions 129 of the gate lines 121 and the endportions 179 of the data lines 171 through the contact holes 181 and182, respectively. The contact assistants 81 and 82 protect the endportions 129 and 179 and enhance the adhesion between the end portions129 and 179 and external devices, such as a gate driving circuit and adata driving circuit.

A partition 361 is formed on the passivation layer 180 and may overlapperipheral portions of the pixel electrode 191.

The partition 361 surrounds the pixel electrodes 191 like a bank, todefine openings 365 to be filled with organic light emitting material.The partition 361 is preferably made of organic or inorganic insulatingmaterial. The partition 361 may be also formed of photoresist includinga black pigment to function as a light blocking member, such that amanufacturing procedure is simplified.

A plurality of light emitting members 370 are formed on the pixelelectrodes 191 and disposed in the openings 365 defined by the partition361. The organic light emitting members 370 are formed using anexemplary embodiment of the inkjet printing system according to thepresent invention. That is, instead of the insulating substrates 210with light blocking members 220 provided on the stage 500, the panelprepared as shown in FIGS. 14 to 16 is provided on the stage 500 forreceipt of material for forming the light emitting members 370 withinthe openings 365. The light emitting members 370 are preferably made oforganic material emitting primary-color lights such as red, green, andblue lights. Thus, the ink 5 is replaced by material for forming thelight emitting members 370. The light emitting members 370, such as red,green, and blue light emitting members 370, are periodically arranged.The OLED represents a desired color by summing the colors from the lightemitting members 370 in space.

Each organic light emitting member 370 may have a multilayeredstructure. For example, the organic light emitting member 370 includesan emitting layer (not shown) emitting light and auxiliary layers (notshown) for improving the efficiency of light emission of the emittinglayer. The auxiliary layers may include an electron transport layer (notshown) and a hole transport layer (not shown) for improving the balanceof the electrons and holes, and an electron injecting layer (not shown)and a hole injecting layer (not shown) for improving the injection ofthe electrons and holes.

A common electrode 270 is formed on the light emitting members 370. Thecommon electrode 270 may further be formed on the partition 361. Thecommon electrode 270 is supplied with the common voltage Vcom. Thecommon electrode 270 may be preferably made of reflective conductorssuch as Al, calcium Ca, barium Ba, and magnesium Mg or alloys thereof ortransparent conductors such as ITO or IZO.

In the above-described OLED, a first gate electrode 124 a connected tothe gate line 121, a first source electrode 173 a connected to the dataline 171, and a first drain electrode 175 a along with a firstsemiconductor island 154 a form a switching TFT Qs having a channelformed in the semiconductor island 154 a disposed between the firstsource electrode 173 a and the first drain electrode 175 a. A secondgate electrode 124 b connected to the first drain electrode 175 a, asecond source electrode 173 b connected to the voltage transmission line172, and a second drain electrode 175 b along with a secondsemiconductor island 154 b form a driving TFT Qd having a channel formedin the semiconductor island 154 b disposed between the second sourceelectrode 173 b and the second drain electrode 175 b. In the switchingTFT Qs and the driving TFT Qd, the gate electrodes 124 a and 124 b formcontrol electrodes, the source electrodes 173 a and 173 b form inputelectrodes, and the drain electrodes 175 a and 175 b form outputelectrodes. The pixel electrodes 191, the organic light emitting members370, and the common electrode 270 form organic light emitting elementsLD. The pixel electrode 191 may be an anode terminal and the commonelectrode 270 may be a cathode terminal. Alternatively, the pixelelectrode 191 may be a cathode terminal and the common electrode 270 maybe an anode terminal. Furthermore, a storage electrode 127 and a voltagetransmission line 172 overlapped with each other form a storagecapacitor Cst.

The OLED emits light upwardly or downwardly with respect to theinsulating substrate 110 to represent the images.

An opaque pixel electrode 191 and a transparent common electrode 270 areused in OLEDs of a top emission type representing the images upwardlywith respect to the insulating substrate 110. A transparent pixelelectrode 191 and a transparent common electrode 270 are used in OLEDsof a bottom emission type representing the images downwardly withrespect to the insulating substrate 110.

Meanwhile, when the semiconductor islands 154 a and 154 b are made ofpolysilicon, the OLED includes intrinsic regions (not shown) disposedopposite with respect to the gate electrodes 124 a and 124 b,respectively and extrinsic regions (not shown) disposed on the intrinsicregions. The extrinsic regions are electrically connected to the inputelectrodes 173 a and 173 b and the output electrodes 175 a and 175 b,and the ohmic contacts 163 a, 163 b, 165 a, and 165 b may be omitted.

While the illustrated embodiment shows the gate electrodes 124 a and 124b disposed between the semiconductors 154 a, 154 b and the insulatingsubstrate 110, in an alternative embodiment, the gate electrodes 124 aand 124 b may be disposed on the semiconductors 154 a, 154 b, such thatthe semiconductors 154 a, 154 b are disposed between the gate electrodes124 a, 124 b and the insulating substrate 110. In this case, the gateinsulating layer 140 is disposed between the semiconductors 154 a, 154 band the control electrodes 124 a and 124 b. Also in such an embodiment,the data conductors 171, 172, 175 a, and 175 b are disposed on the gateinsulating layer 140 and electrically connected to the semiconductors154 a and 154 b through contact holes (not shown) formed on the gateinsulating layer 140. In yet another embodiment, the data conductors171, 172, 175 a, and 175 b are disposed under the semiconductor islands154 a and 154 b and may be connected to the overlaying semiconductorislands 154 a and 154 b.

While semiconductors made of a-Si have been described for use in theOLED, the present invention may also be adopted to OLEDs includingsemiconductors made of polysilicon.

Thus, an inkjet printing system is provided for forming color filters ona color filter layer of an LCD and for forming light emitting members onan OLED. Alignment keys are provided on a panel arranged to receivematerial for forming the color filters or the light emitting members.The alignment keys are sensed by an alignment key position sensor, andthe sensed signals are converted into control signals for properpositioning of a head unit supporting an inkjet head. The alignment keyposition sensor may be provided on the head unit or on an alignment keysensing unit separate from the head unit.

A driving method of the inkjet printing system includes sensingpositions of the alignment keys using the alignment key position sensorto generate sensing signals and using the sensing signals to align aposition of the head unit. The sensing signals may be stored in a memoryfor comparison with a current position of the head unit to generatecontrol signals for aligning the head unit.

By the aligning operation of the head unit using the alignment keys andthe alignment key position sensor, the color filters or light emittingmembers are accurately formed on desired positions of the substrates,thus increasing reliability and decreasing manufacturing cost.

While the present invention has been described in detail with referenceto the preferred embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but, on the contrary, isintended to cover various modifications and equivalent arrangementsincluded within the spirit and scope of the appended claims.

1. An inkjet printing system comprising: a stage on which a substrateincluding at least two alignment keys is mounted; an inkjet head devicedisposed above the stage; and an alignment key sensing device disposedabove the stage, wherein the inkjet head device comprises a head unitincluding an inkjet head, and a supporting unit which supports the headunit and transfers the head unit over the substrate in a firstdirection, and wherein the alignment key sensing device comprises: atleast two alignment key sensors for sensing positions of the alignmentkeys; a sensor supporting unit for supporting the at least two alignmentkey sensors; and a sensor position adjustment device for adjustingpositions of the alignment key sensors in the alignment key sensingdevice, wherein the sensor position adjustment device moves thealignment key sensors so that the first direction which is a movingdirection of the head unit is coincident with a target direction toprint.
 2. The inkjet printing system of claim 1, wherein the sensorposition adjustment device moves the alignment key sensors so that astraight line connecting the at least two alignment key sensors issubstantially perpendicular to the first direction.
 3. The inkjetprinting system of claim 1, wherein the sensor position adjustmentdevice moves the alignment key sensors in two directions which aresubstantially parallel to a surface of the stage and are substantiallyperpendicular to each other with respect to the alignment key sensingdevice.
 4. The inkjet printing system of claim 1, wherein the inkjethead device further comprises a horizontal transporting portion thatmoves the head unit in a second direction which is substantiallyperpendicular to the first direction.
 5. The inkjet printing system ofclaim 1, wherein the alignment key sensing device further comprises atleast two sensor transporting portions moving the at least two alignmentkey sensors in a second direction which is substantially perpendicularto the first direction.
 6. An aligning method of an inkjet printingsystem comprising: a stage; an inkjet head device including a head unitand a supporting unit supporting the head unit; and an alignment keysensing device including at least two alignment key sensors, a sensorsupporting unit supporting the at least two alignment key sensors, and asensor position adjustment device, the method comprising: mounting asubstrate including at least two alignment keys on the stage; sensingthe alignment keys using the alignment key sensors and firstly aligningthe substrate on the stage; examining a first direction in which thesupporting unit moves over the substrate and ink is printed; adjustingpositions of the alignment key sensors in the alignment key sensingdevice using the sensor position adjustment device so that the firstdirection is coincident with a target direction to print; and realigningthe substrate by sending the alignment keys using the position-adjustedalignment key sensors.
 7. The method of claim 6, wherein the adjustingpositions of the alignment key sensors comprises adjusting the sensorposition adjustment device so that a straight line connecting the atleast two alignment key sensors is substantially perpendicular to thefirst direction.
 8. The method of claim 6, wherein the adjustingpositions of the alignment key sensors comprises moving the alignmentkey sensors in two directions which are substantially parallel to asurface of the stage and are substantially perpendicular to each otherwith respect to the alignment key sensing device.
 9. The method of claim6, wherein the inkjet head device further comprises a horizontaltransporting portion that moves the head unit in a second directionwhich is perpendicular to the first direction.
 10. The method of claim6, wherein the alignment key sensing device further comprises at leasttwo sensor transporting portions moving the at least two alignment keysensors in a second direction which is substantially perpendicular tothe first direction.